This invention relates to novel photosensitive compositions. It more particularly refers to polyester-polyether block polymer type photosensitive compositions which are photopolymerizable by the action of actinic light and which are useful in the preparation of relief images, especially relief printing plates.
Unsaturated polyester type photosensitive compositions are already disclosed in, for example, U.S. Pat. No. 2,760,863, and Japanese Pat. Nos. 542,045 and 599,101. Image making articles such as relief plates may be produced by forming a layer of the photosensitive compositions of a desired thickness on a suitable base, exposing the layer to actinic light through, for example, a photographic negative film to photopolymerize the image areas and washing out the non-exposed areas. Relief plates thus obtained may be used as relief printing plates, dry offset printing plates, displays and name plates.
According to these Japanese patents relief printing plates having desired properties can be obtained by suitably selecting the average molecular weight of unsaturated polyesters, the number of ether bonds in the unsaturated polyesters and the type of crosslinking agents. However, with the progress in printing technique printing plates are required to have still higher impact resilience, tear strength, tensile strength, elongation and printing resistance and it has been found difficult to meet these requirements by these methods.
It is known to obtain rubber elastomers by introducing a polyether as a soft segment between two double bonds. It is also known to use a polyether or polyester as the soft segment in the molecular chain of polyurethanes. However, prepolymers containing a polyether along as the soft segment between two double bonds in the molecular chain generally produce relief printing plates having low tensile strength and tear strength and consequently insufficient printing resistance. On the other hand the use of prepolymers containing a polyester alone as the soft segment between two double bonds in the molecular chain slightly improves the tensile strength of relief printing plates as compared with the prepolymers containing a polyether alone as the soft segment but the impact resilience is low and the lack of uniformity in inking and the "fatigue" of plates or deformation of relief images can easily take place. Thus, these defects are fatal especially for flexographic printing plates which require high elastic recovery.
In addition, it is necessary that unexposed portions of photo-sensitive compositions can be readily and easily removed with a solvent liquid. This washing-out property strongly influences the resolution of relief printing plates. The prepolymers containing a polyester alone or a polyether alone as the soft segment do not provide sufficient resolution.
In accordance with this invention, there is provided a photosensitive composition comprising: (1) about 100 parts by weight of at least one prepolymer having a number average molecular weight of about 800 to 20,000 selected from the group consisting of ##EQU1## wherein X.sub.1 represents a residue of an alcohol having one to three ethylenically unsaturated bonds from which the hydroxy group is excluded;
X.sub.2 represents a residue of an amine having one or two ethylenically unsaturated bonds from which the amino group is excluded; PA1 X.sub.3 represents a residue of a carboxylic acid having one ethylenically unsaturated bond from which the carboxy group is excluded; PA1 Y.sub.1,y.sub.2, and Y.sub.3 represent a residue of a diisocyanate respectively, PA1 Q.sub.1,q.sub.2,q.sub.3 and Q.sub.4 each is a residue of a hydroxy terminated block polymer from which the terminal hydroxy groups are excluded and is represented by the formula ##EQU2## i. (A.sup.1) represents a residue of a polyetherdiol having a number average molecular weight of about 200 to 5,000 from which the terminal hydroxy groups are excluded; PA1 2. 0 to about 120 parts by weight of at least polymerizable ethylenically unsaturated monomeric compound; and PA1 3. a photopolymerization initiator in an amount of about 0.001 to 10 weight percent of the total weight of the prepolymer (1) and the polymerizable ethylenically unsaturated monomeric compound (2). PA1 R.sup.14 represents a hydrogen atom, alkyl group having 1 to 4 carbon atoms such as methyl, ethyl, isopropyl or n-butyl, cyclohexyl, phenyl or benzyl group, and one to three of R.sup.10, R.sup.11, R.sup.12, R.sup. 13 and R.sup.14 are hydrogen atoms, PA1 R.sup.16 represents an oxyalkylene group of the formula ##EQU5## or ##EQU6## wherein R.sup.17 represents a hydrogen atom, methyl, monochloromethyl or monobromomethyl group; and f represents an integer of 1 to 20, PA1 R.sup.18 represents an alkylene having 1 to 12 carbon atoms. PA1 a. compounds of the formula ##EQU10## wherein R.sup.15 represents a hydrogen atom or methyl group; PA1 c. compounds of the formula ##EQU13## wherein R.sup.15 represents a hydrogen or methyl group; g is an integer from 2 to 4, and R.sup.15 represents a radical of 2 polyol having g terminal hydroxy groups and a number average molecular weight of at most 1,000, PA1 d. compounds of the formula ##EQU14## wherein R.sup.15 and R.sup.27 each represents a hydrogen atom or methyl group; PA1 e. compounds of the formula ##EQU15## wherein R.sup.15 represents a hydrogen atom or methyl group; PA1 f. aromatic compounds having at least one CH.sub.2 =C&gt; group and one benzene nucleus; and PA1 g. other ethylenically unsaturated monomeric compounds. PA1 i represents an integer from 2 to 10
A.sup.2 represents a residue of a polyethertriol having a number average molecular weight of about 500 to 5,000 from which the terminal hydroxy groups are excluded, PA3 A.sup.3 represents a residue of a polyethertetraol having a number average molecular weight of about 500 to 5,000 from which the terminal hydroxy groups are excluded, PA3 B represents a residue of a saturated polyesterdiol having a number average molecular weight of about 200 to 5,000 from which the terminal hydroxy groups are excluded,
ii A.sup.1 and B; A.sup. 2 and B; A.sup.3 and B; A.sup.1 and A.sup.1 ; B and B, each group is linked with a diisocyanate, PA2 iii the weight ratio of the total weight of A.sup.1 to B, A.sup.2 to B, or A.sup.3 to B is in the range of from about 1:4 to 4:1, PA2 iv. a is an integer from 1 to 4; b is an integer from 1 to 4; c is an integer from 0 to 4; d is an integer from 1 to 3; e is an integer from 1 to 4; x is an integer from 1 to 4; y is 1 or 2; 2 .ltoreq. (a + b) w + c .ltoreq. 20, but c is not zero in the case of the prepolymer (IV) or (V); 2 .ltoreq. d + x .ltoreq. 5, and when e is 1 or 2, y is k or 2; and when e is 3 or 4, y is 1, l, m, n, o, and p, each is an integer from 2 to 6, and k, m, n, o and p is 2 in the case of A.sup.1 ; k, m, n, o, and p each is an integer from 3 to 6 in the case of A.sup.2 ; and k, m, n, o and p each is 4 or 6 in the case of A.sup.3, PA2 ii. trimethylolpropane di-acrylate or -methacrylate, glycerine di-acrylate or -methacrylate and pentaerythritol tri-acrylate or -methacrylate, PA2 iii. allyl alcohol, 2-bromoallyl alcohol 2-chloroallyl alcohol, glycerol diallylether, trimethylolpropane diallyl ether and allyl vinyl carbinol, and ##EQU7## wherein R.sup.15 represents a hydrogen atom or methyl group, and PA2 R.sup.22 represents an alkyl group having 1 to 18 carbon atoms, cyclohexyl, alkoxyalkyl group having at most 15 carbon atoms, cyanoalkyl group having at most 8 carbon atoms, tertiary amino alkyl group having at most 18 carbon atoms, hydrogen atom or oxyalkylene group of the formula ##EQU11## wherein R.sup.17 represents a hydrogen atom, monochloromethyl or monobromomethyl group; and f repesents an integer from 1 to 20, b. compounds of the formula ##EQU12## wherein R.sup.15 represents a hydrogen atom or methyl group; PA2 R.sup.23 and R.sup.24 each represents a hydrogen atom, alkyl group having 1 to 12 carbon atoms, cyclohexyl, benzyl, --R.sup.18 --OH in the case of R.sup.23 being a hydrogen atom, PA2 R.sup.18 represents an alkylene having 1 to 12 carbon atoms, PA2 R.sup.26 represents an alkylene group having up to 6 carbon atoms, PA2 R.sup.28 represents a hydrogen atom, methyl group, monochloromethyl or monobromomethyl group;
The urethane bonds present in the prepolymer greatly affect the tensile strength, elastic recovery, permanent set or "fatigue" of photo-polymerized articles such as relief printing plates, and as the number of urethane bonds increases the tensile strength and elastic recovery after photopolymerization tend to increase. Especially when the number of urethane bonds which are present between A.sup.1 and B; A.sup.2 and B; A.sup.3 and B increases the permanent set after photopolymerization is remarkably improved. When the number of urethane bonds present in Q.sub.1, Q.sub.2, Q.sub.3 or Q.sub.4 is above 40, the hardness and permanent set of photopolymerized articles increase too much to give relief printing plates for practical purposes.
The number average molecular weight of the prepolymer, the number avarage molecular weight of A.sup.1, A.sup.2,A.sup.3 and B, and the total number of urethane bonds which are present between A.sup.1 and B; A.sup.2 and B; A.sup.3 and B; A.sup.1 and A.sup.1 ; and B and B greatly affect the properties of photopolymerized articles. Generally, as the number average molecular weight of the prepolymer increases the mechanical properties of the photopolymerized articles such as tensile strength, tear strength and elongation tend to be improved. On the other hand, as the viscosity of the photosensitive composition containing such a prepolymer with an increased number average molecular weight tends to increase, the processability of the photosensitive composition remarkably diminishes. Thus, the number averge molecular weight of the prepolymer of this invention is typically in the range from about 800 to 20,000. When the number average molecular weight is below 800, there cannot be obtained relief printing plates having sufficient tensile strength and elongation. On the other hand the preparation of prepolymers having an number average molecular weight above about 20,000 becomes difficult and the processability of photosensitive compositions containing such prepolymers extremely diminishes.
In order to produce flexographic printing plates having excellent elastic recovery at low hardness as well as excellent tensile strength, tear strength, elongation and printing resistance, it is preferred to use prepolymers having a number average molecular weight of from about 1,300 to 20,000, and more particularly from about 2,000 to 10,000 and comprising residues (B and A.sup.1, A.sup.2 or A.sup.3) of a polyesterdiol and a polyetherdiol, polyetherdiol, polyethertriol or polyethertetraol having a number average molecular weight of from about 500 to 5,000, and more particularly from about 600 to 4,000 from which the terminal hydroxy groups are exclued, and 2 to 20 urethane bonds in total which are present between A.sup.1 and B; A.sup.1 and A.sup.1 ; B and B; or between A.sup.2 and B; and B and B or between A.sup.3 and B; and B and B.
Also in order to produce printing plates for general purposes such as newspaper printing having high hardness with small permanent set and good flexibility, it is preferred to use prepolymers having a number average molecular weight of about 800 to 20,000 and comprising residues (B and A.sup.1) of a polyesterdiol and a polyetherdiol having a number average molecular weight of from about 800 to 20,000 from which the terminal hydroxy groups are excluded, and 2 to 40 urethane bonds in total which are present between A.sup.1 and B; A.sup.1 and A.sup.1 ; and B and B.
Furthermore, in order to produce relief printing plates for general purposes having a shore hardness D above 35 and good flexibility from the photosensitive compositions having a relatively low viscosity, it is preferred to use prepolymers having a number average molecular weight of from about 800 to 2,000 and comprising residues (B and A.sup.1) of a polyesterdiol and a polyetherdiol having a number average molecular weight of from abut 200 to 500.
Thus, the number average molecular weight of prepolymers, the number average molecular weight of polyesterdiols, polyetherdiols, polyethertriols and polyethertetraols and the total number of the urethane bonds should be chosen depending on the physical properties required for relief structures in accordance with their use and the processability of the photosensitive compositions comprising the prepolymers.
Also the weight ratio of the total weight of A.sup.1 to B; A.sup.2 to B; or A.sup.3 to B, and the kind of A.sup.1, A.sup.2, A.sup.3 and B in the molecular chain of prepolymers greatly affect the tensile strength, tear strength, impact resilience, water resistance and inking of photopolymerized articles and the processability of the photosensitive composition as well as resolution.
In order to obtain good relief printing plates, the weight ratio of the total weight of A.sup.1 to B; A.sup.2 to B; or A.sup.3 to B is in the range of from about 1:4 to 4:1. The preferred range is from 1:4 to 3:1 and the most preferred range is from 1:3 to 2:1.
The polyesterdiols, polyetherdiols polyethertriols and polyethertetraols which may be employed in the preparation of the prepolymers can be produced by conventional methods, and commercially available ones for preparing ordinary urethane resins may be employed in this invention.
The number average molecular weight of the polyesterdiols and polyetherdiols is generally in the range of about 200 to 5,000 and that of the polyethertriols and polyethertetraols is in the range of about 500 to 5,000.
The polyesterdiols are formed by ring opening polymerization of at least one 4-, 6- or 7- membered ring lactone in the presence or absence of a catalyst using a compound such as ethylene glycol.
Examples of suitable 4-, 6- or 7- membered ring lactones include .beta.-propiolactone, .alpha.,.alpha.'-bis (chloromethyl) propiolactone, .gamma.-butyrolactone, .delta.-valerolactone, 3,4, 5-trimethoxy-.delta.-valerdactone, .epsilon.-caprolactone and the derivatives thereof having the formula ##EQU3## wherein R.sup.10, R.sup.11, R.sup.12 and R.sup.13, each represents a hydrogen atom, alkyl group having 1 to 4 carbon atoms such as methyl, ethyl isopropyl or n-butyl group, cyclohexyl, methoxy, ethoxy, phanyl or benzyl group;
including, for examples, .gamma.-methyl-.epsilon.-caprolactone and 4-methyl-7-isopropyl-.epsilon.-caprolactone.
Also the polyesterdiols are formed by direct esterirication, ester exchange or addition between at least one diol and at least one saturated dicarboxylic acid and/or its anhydride and/or dimethyl or diethyl ester thereof is a mole ratio of OH/COOH &gt; 1.
Examples of suitble diols include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,3-butanediol, 1,2-dimethyl ethylene glycol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, diethylene glycol and dipropylene glycol.
Examples of suitable saturated dicarboxylic acids, anhydrides and methyl or ethyl esters thereof include oxalic acid, malonic acid, methyl malonic acid, succinic acid, methyl succinic acid, glutaric acid, 3-methyl glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dimethyl or diethyl esters thereof, and anhydrides thereof.
Typical polyesterdiols are poly-.delta.-valerolactone diol, poly-.epsilon.-caprolactone diol, poly-.gamma.-methyl-.epsilon.-caprolactonediol, polyethylene adipatediol, polypropylene adipatediol, polybutylene adipatediol, polyhexamethylene adipatediol and polyethylene succinatediol.
Of these polyesterdiols polypropylene adipatediol is preferably employed for producing flexographic printing plates having low hardness. Als polypropylene adipatediol is effective for preventing the photosensitive composition comprising the prepolymer obtained therefrom from crystalizing at low temperatures due to its low melting point.
Up to about 30 percent by weight of the polyesterdiol may be substituted with polybutadienediols having a number average molecular weight of about 200 to 5,000.
These polyesterdiols may be modified by having their chain lengths extended through reaction with a diisocyanate.
Examples of suitable polyetherdiols are polyethylene glycoldiol, polypropylene glycoldiol, poly-1,4-oxbutylene glycldiol, dihydroxy-terminated ethylene oxide-propylene oxide copolymers (either block copolymers or random copolymers), polyepichlorohydrindiol, polyethylene glycol triol and polyethylene glycol tetraol.
In general, the polyetherdiols, polyethertriols and polyethertetraols are formed by condensation polymerization between ethylene oxide or propylene oxide and a compound having at least two active hydrogens such as ethylene glycol, propylene glycol, glycerine, trimethylolpropane, 1,2,6-hexanetriol, pentaerythritol or ethylene diamine in the presence of an alkali catalyst.
The above-described polyetherdiols may be modified by having their chain lengths extended through reaction with diisocyanate.
Of those polyetherdiols especially when ethylene oxide-propylene oxide copolymers having about 20 to 80 weight percent of ethylene oxide units are employed as the polyetherdiol there can be prepared flexographic printing plates having excellent strength, impact resilience and elastic recovery in spite of extremely low hardness using the photosensitive composition comprising the prepolymer, and also the unexposed portions of the photosensitive composition after photopolymerization can be effectively and advantageously washed out by an aqueous surfactant solution.
The ethylene oxid-propylene oxide copolymers may be either random copolymers or block copolymers but the block copolymers are more preferred in order to obtain the desired effects.
Furthermore, the combination of a polyethylene adipatediol as the polyesterdiol and a dihydroxy-terminated ethylene oxide-propylene oxide copolymer having about 20 to 80 weight percent of ethylene oxide units as the polyetherdiol is especially effective for further lowering of the hardness after photopolymerization of the photosensitive composition comprising the prepolymer obtained therefrom, maintaining the viscosity of photosensitive composition at a low, value preventing the photosensitive composition from crystallizing at low temperatures, simplifying production of printing plates and reducing almost to zero the change in hardness with the lapse of time after photopolymerization of the photosensitive composition. Thus, this combination can provide photosensitive compositions having superior properties for flexographic printing plates.
At least one polyesterdiol or chain-extended polyesterdiol and at least one polyetherdiol or chain-extended polyetherdiol, polyethertriol or polyethetetraol are linked through reaction with a diisocyanate at a temperature of generally about 40.degree.C. to 120.degree.C., and preferably about 50.degree.C. to 100.degree.C in an inert gas atmosphere such as nitrogen gas in the presence or absence of a catalyst in a mole ratio of OH/NCO &lt; 1 or OH/NCO &gt; 1. The catalysts include, for example, tertiary amines such as N,N-dimethylbenzyl amine, N,N-dimethyllaurylamine and triethylene diamine (diazabicyclooctane), and organo-heavy-metal compounds soluble in the reaction system such as ferrous acetoacetate, dibutyltin dilaurate, dibutyltin di-2-hexoate, stannous oleate and stannous octoate.
When the chain-extending reaction is effected in a mole ratio of OH/NCO &lt; 1 the terminals of the chain-extended polymers which are polyesterpolyether block polymers, are isocyanate groups. On the other hand when the chain-extending reaction is effected in a mole ratio of OH/NCO &gt; 1 terminals of the polyester-polyether block polymers are hydroxy groups.
Conventionally the polyester-polyether block polymers are prepared by firstly effecting reaction between a diisocyanate and, for example, a polyesterdiol in a mole ratio of OH/NCO &lt; 1 and secondly effecting reaction between the resulting isocyanate-terminated polyester and a polyetherdiol, polyethertriol or polyethertetraol in a mole ratio of OH/NCO &lt; 1 or OH/NCO &gt; 1. When a polyetherdiol, polyethertriol or polyethertetraol is employed instead of the polyesterdiol in the first reaction, a polyesterdiol is employed in the second reaction.
Exemplary diiscyanates which may be employed in the preparation of the chain-extended polyesterdiols, chain-extended polyetherdiols and polyester-polyether block polymers include 2,4-tolylene diisocyanate, 2,6-toylene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 1,3-dimethylphenyl-2,4-diisocyanate, 1,3-dimethylphenyl-4,6-diisocyanate, 1,4-dimethylphenyl-2,5-diisocyanate, 1-chlorophenyl-2,4-diisocyanate, 4,4'-diphenyl diisocyanate, 2,4'-diphenyl diisocyanate, 3,3'-dimethoxy-4,4'- diphenylmethane diisocyanate, 3,3'-dimethyl-4,4'-diphenylmethane diisocyanate, 1,4-naphthylene diisocyanate, 1,5-naphthylene diisocyanate, 2,6-naphthylene diiocyanate, 2,7-naphthylene diiocyanate, p-xylylene diisocyanate, m-xylylene diisocyanate, 1,4-tetramethylene diisocyanate, 1,5-pentamethylene diisocyanate, 1,6-hexamethylene diisocyanate, 1,7-heptamethylene diisocyanate, 1,8-octamethylene diisocyanate, 1,9-nonamethylene diisocyanate, 1,10-decamethylene diisocyanate, 2,2,4-trimethyl-1,5-pentamethylene diisocyanate, 2,2'-dimethyl-1,5-pentamethylene diisocyanate, 3-methoxy-1,6-hexamethylene diisocyanate, 3-butoxy-1,6-hexamethylene diisocyanate, .omega., 107'-dipropylether diisocyanate, 1,4-cyclohexyl diiocyanate, 1,3-cyclohexyl diisocyanate and mixtures of these diisocyanates. Also triisocyanates such as triphenylmethane-4,4',4"-triisocyanate, adduct of trimethylolpropane and 2,4-tolylene diisocyanate, adduct of trimethylol-propane and 1,6-hexamethylene diisocyanate may be employed in the similar manner as polyethertriols.
The prepolymers of this invention may be prepared by effecting reaction between the polyester-polyether block polymer whose terminals are isocyanate groups and one compound selected from the group consisting of (I) an alcohol having one to three ethylenically unsaturated bonds, (II) an amine having one to two ethylenically unsaturated bonds and (III) a carboxylic acid having one ethylenically unsaturated bond.
Examples of suitable alcohols (I) include (i) a compound selected from the group consisting of ##EQU4## wherein R.sup.15 represents a hydrogen atom or methyl group,
Examples of suitable compounds (i) include 2-hydroxyethyl acrylate or methacrylate, 2-hydroxypropyl acrylate or methacrylate, 3-bromo-2-hydroxypropyl acrylate or methacrylate, 3-chloro-2-hydroxypropyl acrylate or methacrylate, 4-hydroxy-n-butyl acrylate or methacrylate, diethylene glycol monoacrylate or monomethacrylate, dipropylene glycol monoacrylate or monomethacrylate, dibutylene glycol monoacrylate or methacrylate, tetraethylene glycol monoacrylate or methacrylate, monoacrylates or methacrylates of polyoxyethylene diols having a number average molecular weight of about 200 to 900, monoacrylates or monomethacrylates of polyoxypropylene diols having a number average molecular weight of about 200 to 1,200 and monoacrylates or monomethacrylates of polyoxybutylene diols having a number average molecular weight of about 200 to 1,500, 3-bromo-2-hydroxypropyl acrylate or methacrylate, 3-chloro-2-hydroxypropyl acrylate or methacrylate and ##EQU8## Of all compounds (i) when a compound of the formula ##EQU9## wherein R.sup.15 and R.sup.17 are the same as defined above; and h is an integer of 2 to 20 and especially 4 to 10,
is used, there can be obtained printing plates having excellent impact resilience at low hardness which are useful for flexographic printing on corrugated cardboards. Furthermore, the prepolymers containing the residue of the compound represented by this formula can be more readily and easily washed out by an aqueous alkali solution or an aqueous surfactant solution and accordingly the resolution can be remarkably improved. Also the resulting photopolymerized articles have excellent resistance to water.
Examples of suitable compounds (iv) include N-methylol acrylamide or methacrylamide, 2-hydroxyethyl acrylamide or methacrylamide, 2-hydroxypropyl acrylamide or methacrylamide 4-hydroxy-n-butyl acrylamide or methacrylamide and the products obtained by ester-amide exchange reaction between methyl acrylate or methacrylate and an amino alcohol having at most 12 carbon atoms.
Examples of suitable amines (II) are allylamine and diallylamine.
Examples of suitable carboxylic acids (III) are acrylic acid, methacrylic acid and itaconic acid.
The prepolymers of this invention may also be prepared by effecting reaction between the polyester-polyether block copolymer whose terminals are hydroxy groups and a compound selected from the group consisting of (IV) and/or (V) itaconic anhydride and acrylic acid, methacrylic acid, acrylic anhydride, methacrylic anhydride, acrylic chloride and methacrylic chloride.
The photosensitive compositions of this invention comprise at least one prepolymer and a photopolymerization initiation in an amount of about 0.001 to 10 weight percent of the prepolymer.
The photosensitive compositions may contain at least one polymerizable ethylenically unsaturated monomeric compound in an amount up to about 120 parts by weight based on 100 parts by weight of the prepolymer.
Examples of suitable polymerizable ethylenically unsaturated monomeric compounds include
wherein
Exemplary compounds (a) include methyl acrylate or methacrylate, ethyl acrylate or methacrylate, isopropyl acrylate or methacrylate, n-butyl acrylate or methacrylate, n-pentyl acrylate or methacrylate, n-octyl acrylate or methacrylate, 2-ethylhexyl acrylate or methacrylate, cyclohexyl acrylate or methacrylate, lauryl acrylate or methacrylate, isodecyl acrylate or methacrylate; methoxymethyl acrylate, ethoxybutyl acrylate or methacrylate, 2-methoxypropyl acrylate or methacrylate, n-butoxymethyl acrylate or methacrylate; cyanomethyl acrylate or methacrylate, cyanobutyl acrylate or methacrylate; (N,N-dimethylamino)methyl acrylate or methacrylate, 2-(N,N-dimethylamino)ethyl acrylate or methacrylate, 2-(N,N-diethylamino)ethyl acrylate or methacrylate, 2-(N,N-benzylamino)ethyl acrylate or methacrylate, 2-(N,N-diethylamino) propyl acrylate or methacrylate; acrylic acid, methacrylic acid, and the same compounds (i) as described afore.
Of these compound when about 10 to 100 parts by weight, based on 100 parts by weight of the prepolymer, of a compound of the formula ##EQU16## wherein R.sup.15 and R.sup.17 are the same as defined hereinabove; and
is employed, the resulting photopolymerized articles have superior impact resilience and elastic recovery. Especially desirable results are realized when i is an integer from 4 to 6 in the above-described formula.
Exemplary compounds (b) include acrylamide, methacrylamide, N,N-dimethyl acrylamide or methacrylamide, N,N-diethyl acrylamide or methacrylamide, N,N-diisopropyl acrylamide or methacrylamide, N,N-didecylacrylamide or methacrylamide, N-isopropyl acrylamide or methacrylamide, N-cyclohexyl acrylamide or methacrylamide, N-benzyl acrylamide or methacrylamide, and the same compounds (iv) as described above.
Exemplary compounds (c) include ethyleneglycol di-acrylate or -methacrylate, diethyleneglycol di-acrylate or -methacrylate, triethyleneglycol di-acrylate or -methacrylate, tetraethyleneglycol di-acrylate or -methacrylate, polyethyleneglycol (number average molecular weight: 200 to 1,000)di-acrylate or -methacrylate, propyleneglycol di-acrylate or -methacrylate, dipropyleneglycol di-acrylate or -methacrylate, polypropyleneglycol (number average molecular weight: 100 to 1,000) di-acrylate or -methacrylate, butyleneglycol di-acrylate or -methacrylate, trimethylolethane tri-acrylate or -methacrylate, trimethylolpropane tri-acrylate or -methacrylate and pentaerythritol tetra-acrylate or -methacrylate.
Exemplary compounds (d) include N,N'-methylenebisacrylamide, N,N'-methylenebis-methacrylamide, N,N'-trimethylenebisacrylamide, N,N'-trimethylenebismethacrylamide, N,N'-hexamethylenebisacrylamide and N,N'-hexamethylenebismethacrylamide.
Exemplary compounds (e) include 2-acid phosphoxyethyl acrylate or methacrylate, 3-chloro-2-acid phosphoxypropyl acrylate or methacrylate and 3-bromo-2-acid phosphoxypropyl acrylate or methacrylate.
These compounds increase the photosensitivity of the photosensitive compositions and prevent the photosensitive compositions from diminishing in photosensitivity with the lapse of time, and furthermore improve the inking of photopolymerized articles especially having a Shore hardness D of more than 35. These compounds are preferably employed in an amount of about 0.001 to 1 parts by weight based on 100 parts of the prepolymer.
Exemplary compounds (f) include styrene, alpha-methylstyrene, alpha-chlorostyrene, p-tert-butylstyrene, p-sec-butylstyrene, aminostyrene, methoxystyrene, vinyltoluene, vinylbenzoic acid, vinylphenol, allylbenzene, allyltoluene, monoallylphthalate, divinylbenzene.
Exemplary compounds (g) include vinylacetate, vinylpropionate, vinyllaurate, methylvinyl benzoate, beta-hydroxyethyl vinyl benzoate, vinyl succinate, vinyl adipate, divinylphthalate, divinylterephthalate, and the same alcohols (ii) as described above.
The amount and kind of the polymerizable ethylenically unsaturated monomeric compounds are suitably selected depending upon the properties of photopolymerized articles in accordance with their use and the processability of the photosensitive compositions containing such monomeric compounds.
It is necessary that the reaction of photosensitive compositions is initiated only by the action of actinic light and that they are thermally stable. Therefore, preferably polymerization initiators are thermally inactive below 40.degree.C and initiate photopolymerization upon irradiation with actinic light.
Exemplary photopolymerization initiators include benzoins such as benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, alpha-methylbenzoin, alpha-ethylbenzoin, alpha-methyl benzoin methyl ether, alpha-phenylbenzoin, alpha-allylbenzoin; anthraquinones such as anthraquinone, chloroanthraquinone, methylanthraquinone, ethylanthraquinone, tertiary butylanthraquinone; diketones such as benzil, diacetyl; phenones such as acetophenone, benzophenone, omega-bromoacetophenone; 2-naphthalene sulfonyl chloride; disulfides such as diphenyl disulfide, tetraethylthiouram disulfide; dyes such as Eosin G (C.I. 45380) and Thionine (C.I. 52025); and the like.
These photopolymerization initiators are typically used in an amount of from 0.001 to 10 weight percent, and preferably about 0.01 to 4 weight percent of the total weight of the prepolymer and the polymerizable ethylenically unsaturated monomeric compound.
Known stabilizers may be employed for the purpose of maintaining storage stability (shelf life) of the photosensitive compositions. Such stabilizers may be added when the components of a photosensitive composition are admixed or may be added to each component separately prior to admixing of the components.
Exemplary stabilizers include hydroquinone, monotert-butyl hydroquinone, 2,5-di-tert-butyl hydroquinone, catechol, tert-butyl catechol, benzoquinone, 2,5-diphenyl-p-benzoquinone, p-methoxy phenol, picric acid and di-p-fluorophenylamine.
These stabilizers are added only for preventing thermal polymerization without the actinic radiation set forth above without restraining the photopolymerization reaction. Consequently the amount of the stabilizers may be preferably about 0.001 to 2.0 percent by weight of the total weight of the prepolymer and the polymerizable ethylenically unsaturated monomeric compound.
Furthermore, various compounds such as plasticizers and softeners may be incorporated into the photosensitive compositions in order to improve the mechanical properties after photopolymerization. These compounds include, for example, dioctylphthalate, butylphthalyl butylene glycolate, polyester type plasticizers, epoxy type plasticizers, various phosphates and polyethers such as polypropylene glycol.
The photosensitive compositions may additionally contain unsaturated polyester type prepolymers and polyethers having a number average molecular weight of from about 1,000 to 20,000 and polymerizable ethylenic double bonds such as copolymers of propylene oxide and allyl glycidyl ether.
The photosensitive compositions of this invention are photopolymerized by actinic radiation having wave lengths of 2,000 to 8,000 Angstroms. Practical sources of such actinic radiation include carbon arc lamps, super high pressure mercury lamps, high pressure mercury lamps, low pressure mercury lamps, xenon lamps, ultra violet fluorescent lamps and sunlight.
When the photosensitive compositions of this invention are exposed to actinic light through a process transparency, e.g., a negative or positive film, the areas corresponding to the transparent image portions are photopolymerized in about 1 second to 60 minutes and the non-image areas, i.e. unexposed areas, remain substantially unphotopolymerized. These non-exposed areas may be washed away with a solvent liquid such as water, an aqueous solution, an aqueous surfactant solution or an organic solvent. Exemplary solvent liquids include aqueous solutions of sodium hydroxide, potassium hydroxide, calcium hydroxide, ammonium hydroxide, sodium carbonate, sodium bicarbonate, potassium carbonate, hydrochloric acid, sulfuric acid, nitric acid, acetic acid; aqueous solutions of methanol, ethanol, isopropanol and acetone; methanol, ethanol, isopropanol, acetone, methylethyl ketone, ethyl acetate, butyl acetate, dioxane, tetrahydrofurane, phenol, ether, benzene, toluene, gasoline, kerosene, light oil, trichloroethylene or mixtures thereof; an aqueous solution of surfactants such as anionic, cationic, amphoteric or nonionic surfactants. Of these surfactants it is preferred to use anionic surfactants such as sodium or potassium salt of saturated or unsaturated fatty acids having 12 to 18 carbon atoms or alkylbenzene sufonic acids.
One of the characteristics of this invention is that the photosensitive compositions according to this invention can be washed out by such aqueous surfactant solutions.
For example a relief printing plate may be prepared by placing a process transparency, e.g., a negative film, on a glass sheet transparent to actinic light, covering the negative film with a film transparent to actinic light such as polyester film, depositing the photosensitive composition upon the film to form a layer of 0.1 mm to 10 mm. in thickness, placing a base or support material such as polyester film on the layer according to the process and apparatus described in German DOS Pat. No. 2,029,238, putting a glass sheet transparent to actinic light on the support material, exposing the resulting assembly to actinic light, first from the support material side, second from the negative film side or simultaneously from the support material side and the negative film side or from the negative film side in case of metal support materials or opaque support materials, removing the glass sheets, the negative film and the film covering the negative film from the assembly, washing out the unexposed portions of the layer, drying the resulting relief printing plate and, if necessary, postexposing the whole relief printing plate.
Examples of suitable base or support materials include metals such as steel and aluminum plates, sheets and foils and plastics such as polyester, polyamide, polyvinylchloride, polyvinylidenechloride, polymethylmethacrylate, polystyrene and cellulose ester films and plates. These support materials may be either transparent or opaque to actinic light. The thickess of these support materials is preferably in the range of 0.1 mm. to 2.0 mm. for metal plates, sheets and foils and preferably in the range of 50 microns to 2 mm. for plastic films and plates.